1. Field of the Invention
The present invention generally relates to anchoring systems for securing an implanted tubular medical device to a patient, and more particularly, to such anchoring systems for securing intracranial tubular medical devices to the patient's skull.
2. Description of the Prior Art
Surgical procedures of a patient's brain often require implanting a medical device to a prescribed intracranial target site. The implanted medical device typically requires long-term communication between the target site and a remote site located outside the patient's skull. The device can be electrically-based wherein power or signal lead wires must link the device at the target site to the outside world, or the device may be a catheter implanted to administer a drug from a remote location precisely at the target site within the brain or perhaps positioned to shunt fluid from the target site, or a catheter that includes mapping or stimulating electrodes at its distal end.
Either the electrical lead or the catheter reaches the brain by passing through a predrilled hole in the patient's skull, called a burr hole.
Electrical stimulation of the brain can be used for a variety of therapeutic treatments including relief of chronic pain and control of movement disorders. A typical electrical brain-stimulation system includes a pulse generator operatively connected to at least one electrode by a lead. The lead is connected to the electrodes at its distal end. The electrodes are implanted within the patient's brain at a precise location to optimize the applied stimulation. The lead is connected to the pulse generator at its proximal end. To prevent dislodging the implanted distal end of each electrode, a portion of the lead must be anchored in position, usually at the point of entry, the burr hole.
It is also common to use catheters to either introduce fluids (such as drugs) to or collect biological fluids from a specific target site within the patient's brain to treat brain disorders such as malignancies or neurodegenerative diseases. Another example is to position an implantable deep-brain infusion catheter in the striatum or putamen to deliver a pharmaceutical agent to treat movement disorders such as Parkinson's Disease. Typically, these implantable catheters are vary delicate being only about 1 mm to 1.5 mm in outer diameter and are therefore prone to kinking and abrasive damage during handling and especially during use over their lifetime. As with the above-described electrical application, the delicate catheter must be secured so that the distal portion of the catheter remains at the target site within the brain, regardless of the patient's movement or the movement of the catheter outside the brain, and also must prevent or at least discourage trauma that may kink or otherwise damage the catheter.
In order to insert the lead or catheter into the patient's brain, a surgeon first drills a hole in the patient's cranium using a surgical burr or a cranial perforator. The hole size will vary depending on the particular procedure being performed. The drill cuts a clean straight hole into the patient's skull and often leaves a sharp edge along the upper rim of the burr hole. Any inserted lead or catheter must be protected from this sharp edge. To do this, a burr hole ring is often inserted into the burr hole before the catheter or lead wire is inserted through the hole into the patient's brain to the target site. This ring is often used to cooperate with an insert to anchor the exiting catheter or lead wire. Previously, intracranial catheters have been sutured directly to the periosteum, which is a fibrous membrane covering the surface of bone. The periosteum does not provide as much stability as desired, and movement of the catheter anchor may result in displacement of the catheter tip.
Another method of attaching a catheter tube to a patient included the steps of first coiling the tube to form a loop, applying a strip of adhesive tape over the loop and attaching the opposite ends of each strip of tape to the patient's skin. The function of the loop was to act as a strain-relief so that the implanted distal end of the catheter tube is not displaced or disturbed even when unexpected tension is applied to the tubing.
For situations wherein an implanted intracranial medical device must remain operational for long periods of time, it is even more important to safely and effectively anchor the leads and/or catheters to a patient's skull to prevent displacement of the distal ends within the patient's brain regardless of the relative motions of these leads and/or catheters outside the patient's skull.
Obviously, a patient with such intracranial leads and/or catheters in place, whether in a hospital recovery ward, or leading an active life will invariably challenge the integrity and strength of the anchoring system. Typically, during normal patient activities, the communicating leads located outside the patient's skull will become entangled and snagged on various things and will become tugged or even violently jerked. The anchoring system must be strong enough to resist such trauma to the delicate catheter and also prevent dislodgement of the distal tip from the target site. To achieve this, current anchors are often secured directly to the patient's skull using fasteners or an appropriate adhesive or both.
One system for fixing a cranial lead is disclosed in U.S. Pat. No. 4,328,813. This patent discloses a socket and plug anchoring system wherein the lead is engaged by and held within a neck portion of the socket and recessed portion of the plug. However, in this arrangement the lead may easily be moved, particularly axially, when the plug is forced into engagement with the socket. This system uses the shape of the plug to force the exiting lead into a friction bend. This system cannot be used with catheters and any tension applied to the remote portions of the leads will act to directly remove the plug and also the socket, which will then release the lead and easily risk displacement of its distal end. This system fails to offer any strain-relief structure that allows remote applied tension to the leads to be absorbed without dislodging the implanted distal ends from the target site.
Another brain-lead anchoring system is disclosed in U.S. Pat. No. 5,464,446, “Brain Lead Anchoring System,” assigned to Medtronic, Inc., which is incorporated herein by reference. The anchoring system of this referenced patent includes several parts, a plug, a cap and a socket, that must all be assembled by the surgeon and secured within the burr hole of the patient's skull and around either a lead or a catheter. A plug and socket use mere friction within the burr hole to hold the anchor and lead in place to the patient's skull. The cap covers the burr hole and allows two exiting passages. A first one is sharply angled for a lead wire and a second passage that is straight for accommodating catheters, which cannot handle the sharp bend of the first passage.
Although the anchoring system of U.S. Pat. No. 5,464,446 is versatile by allowing both a lead wire and a catheter to exit a patient's skull atraumatically, the device is too difficult to assemble, will not hold up to even moderate applied tension, and forces a catheter to exit normal to the patient's skull thereby causing difficultly in allowing the patient to perform normal activities or even hide their medical disposition—for example, the patient cannot wear a hat without potentially kinking or damaging the catheter. Also, the device of this prior art patent fails to offer a strain-relief function that can mitigate the displacement of the distal end of the implanted lead or catheter due to remote applied tension.